https://ies.ed.gov/ncee/wwc/Document/33#/typesout
"In addition, if there is evidence that the populations were drawn from very different settings, the principal investigator may decide that the environments are too dissimilar to provide an adequate comparison. The High School Mathematics review team also will examine other baseline characteristics (when available) to assess baseline equivalence of studies. These characteristics include, but are not limited to, the following:
- Gender
- Socioeconomic status
- Racial/ethnic breakdown
- Percentage of English as a second language students
- Percentage of bicultural students
- “At-risk” status (as provided by study authors)
- Location of the schools involved
- Homogeneous groupings of students
- School type (public, private, religious)
- School SES (e.g., Title I school)
- Average class size (small, medium, large)
- Average teacher characteristics (e.g., teacher education and experience)
- School size
The provision of all such information, however, is not a requirement of the review."